Shear Strength Envelopes of Biocemented Sands with Varying Particle Size and Cementation Level

Microbial-induced calcium carbonate precipitation (MICP) is a bio-mediated technique that may be used to improve the strength and stiffness of soils. Various parameters affect the behavior of MICP-cemented sand, and their effects must be explored before upscaling the MICP treatment technique. The study presented herein investigates the shear response of three types of sand (Ottawa 20-30, Ottawa 50-70, and Nevada) sheared in drained triaxial compression under three effective confining pressures (10, 100, and 400 kPa) at four levels of cementation (untreated, light, moderate, and heavy). Measurements of shear wave velocity were used for process monitoring throughout biotreatment. Shear wave velocity was used as an index to represent the cementation levels. After shearing, the calcium carbonate content was measured directly. Treated specimens showed similar shear responses at a given cementation level, although the number of treatments and the mass of precipitated calcium carbonate varied widely. Bilinear and nonlinear failure envelopes are proposed based on the obtained results to estimate the shear strength of MICP-treated sand. The shear strength parameters are estimated based on the developed bilinear failure envelope. SEM images were used to visually track the evolution of cementation at different cement contents. The predominant crystal phase of precipitated calcium carbonate was visually identified to be calcite.